Role of IGFs in the transformation of several cancer cells is by now well established. Both IGFs (IGF-I and IGF-II) are potent mitogenic agents for several normal and neoplastic cells. IGF binding proteins (IGF-BPs), on the other hand are believed to modulate the mitogenic effects of IGFs. Within the past two years we and others have established that primary human colon cancers and established colon cancer cell lines express and secrete the mitogen, IGF-II, and the modulating proteins, IGF-BPs. It is, however, not known if IGFs and IGF-BPs play a major role in the growth and differentiation of colon cancer cells. It is speculated that the mitogenic potential of a colon cancer cell line will depend upon the relative expression of the mitogen and the modulator. The major hypothesis of this grant proposal therefore is that the relative expression and secretion of IGF-II and IGF-BPs dictates the growth differentiation potential of colon cancer cells. Our major strategy is to investigate the individual role of IGF-II and IGF-BPs in the growth and differentiation of colon cancers. Towards this goal we will use stable and inducible transfectants that either express the sense or the antisense form of the mitogen/modulatory proteins to confirm the relative role of IGFs and IGF-BPs in initiating or supporting the proliferative/differentiated state of the cells. Alternatively, we will measure the effect of IGF peptides, specific antibodies and antisense oligonucleotides on proliferation of a representative colon cancer cell line (Colo-205) (that does not differentiate in culture), and differentiation of a representative colon cancer cell line (CaCo2 cells) (that spontaneously differentiates in culture). In a second set of studies, the proliferation of colon cancer cells will be measured in vivo in specific mouse models, in the presence or absence of IGFs, IGF-BPs and IGF-receptor antagonists. Alternatively, growth and differentiation of cancer cells, transfected with vectors expressing the sense or antisense IGFs and BPs, will be measured in nude mice. These studies will help us to define the role of circulating vs autocrine (endogenous) IGFs and IGF- BPs in the growth and differentiation of colon cancers in vivo. At the end of these studies we expect to have defined the mitogenic/differentiation potential of IGFs in the presence of modulating IGF-BPs. The results of these studies will help us to move a step closer towards our overall goal of understanding the role of the IGF system in the proliferation and differentiation of neoplastic colonic mucosal cells, and provide the basic information for developing more appropriate, clinically relevant, protocols.